Storage controllers and storage control methods

ABSTRACT

According to various embodiments, a storage controller configured to control storage of data in a pre-determined area of a storage medium may be provided. The storage controller may include a memory configured to store a write pointer, a reclaim pointer, and a wrapped around pointer. The write pointer may indicate a location of the storage medium to write incoming data. The reclaim pointer may indicate a location of the storage medium to perform a space reclamation. The wrapped around pointer may indicate a location of the storage medium where writing is to continue if writing of data reaches an end of the pre-determined area.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of the U.S. provisionalpatent application No. 61/715,344 filed on 18 Oct. 2012, the entirecontents of which are incorporated herein by reference for all purposes.

TECHNICAL FIELD

Embodiments relate generally to storage controllers and storage controlmethods.

BACKGROUND

Amounts of data to be stored are increasing. Thus, there may be a needfor efficient storage of data.

SUMMARY

According to various embodiments, a storage controller configured tocontrol storage of data in a pre-determined area of a storage medium maybe provided. The storage controller may include a memory configured tostore a write pointer, a reclaim pointer, and a wrapped around pointer.The write pointer may indicate a location of the storage medium to writeincoming data. The reclaim pointer may indicate a location of thestorage medium to perform a space reclamation. The wrapped aroundpointer may indicate a location of the storage medium where writing isto continue if writing of data reaches an end of the pre-determinedarea.

According to various embodiments, a storage control method ofcontrolling storage of data in a pre-determined area of a storage mediummay be provided. The storage control method may include controlling amemory to store a write pointer, a reclaim pointer, and a wrapped aroundpointer. The write pointer may indicate a location of the storage mediumto write incoming data. The reclaim pointer may indicate a location ofthe storage medium to perform a space reclamation. The wrapped aroundpointer may indicate a location of the storage medium where writing isto continue if writing of data reaches an end of the pre-determinedarea.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. The drawings are not necessarilyto scale, emphasis instead generally being placed upon illustrating theprinciples of the invention. In the following description, variousembodiments are described with reference to the following drawings, inwhich:

FIG. 1A and FIG. 1B show storage controllers according to variousembodiments;

FIG. 1C shows a flow diagram illustration a storage control method;

FIG. 2 shows an illustration the internals of a hybrid hard disk driveaccording to various embodiments;

FIG. 3 shows different types of data that can be stored in theNon-volatile memory (NVM) of the hybrid shingled writing disk accordingto various embodiments;

FIG. 4 shows an illustration of an overview of a hybrid shingled diskaccording to various embodiments;

FIG. 5 shows a logical block diagram describing the architecture of thevarious components of the hybrid shingled writing disk according tovarious embodiments;

FIG. 6 shows an illustration of a data band design and layout accordingto various embodiments;

FIG. 7 shows an illustration of how a track is divided into various datablocks and how partial blocks form up a logical track according tovarious embodiments;

FIG. 8 and FIG. 9 show illustrations of the information that is requiredfor the logical-to-physical mapping of the blocks according to variousembodiments;

FIG. 10 shows an illustration of the invalid block information forindicating which blocks in the data bands contain invalid/validinformation according to various embodiments;

FIG. 11 shows that a data band contains a write pointer to indicatewhere to append the next block and a wrapped-around point for indicatingwhere to wrapped around new appends when the end of the data band isreached according to various embodiments;

FIG. 12 shows a data band that has been partially reclaimed and writesthat has been wrapped around according to various embodiments;

FIGS. 13A and 13B illustrate how inactive data is kept at the top of thedata band and reclaim and new appends begins after the inactive dataregion according to various embodiments; and

FIG. 14 shows an illustration of a multilevel map according to variousembodiments.

DESCRIPTION

Embodiments described below in context of the devices are analogouslyvalid for the respective methods, and vice versa. Furthermore, it willbe understood that the embodiments described below may be combined, forexample, a part of one embodiment may be combined with a part of anotherembodiment.

In this context, the storage controller as described in this descriptionmay include a memory which is for example used in the processing carriedout in the storage controller. A memory used in the embodiments may be avolatile memory, for example a DRAM (Dynamic Random Access Memory) or anon-volatile memory, for example a PROM (Programmable Read Only Memory),an EPROM (Erasable PROM), EEPROM (Electrically Erasable PROM), or aflash memory, e.g., a floating gate memory, a charge trapping memory, anMRAM (Magnetoresistive Random Access Memory) or a PCRAM (Phase ChangeRandom Access Memory).

In an embodiment, a “circuit” may be understood as any kind of a logicimplementing entity, which may be special purpose circuitry or aprocessor executing software stored in a memory, firmware, or anycombination thereof. Thus, in an embodiment, a “circuit” may be ahard-wired logic circuit or a programmable logic circuit such as aprogrammable processor, e.g. a microprocessor (e.g. a ComplexInstruction Set Computer (CISC) processor or a Reduced Instruction SetComputer (RISC) processor). A “circuit” may also be a processorexecuting software, e.g. any kind of computer program, e.g. a computerprogram using a virtual machine code such as e.g. Java. Any other kindof implementation of the respective functions which will be described inmore detail below may also be understood as a “circuit” in accordancewith an alternative embodiment.

Amounts of data to be stored are increasing. Thus, there may be a needfor efficient storage of data.

Hybrid disks may include both a rotating media and some fasternon-volatile memory (NVM) for temporary and medium term/frequentlyaccessed data storage. Most of the data may be stored on the rotatingmedia and the capacity of the NVM is only a small percent of thecapacity of the rotating media.

Hybrid disks may use the NVM to improve performance and/or reduce powerconsumption. Operating system data and some application data may bestored in the NVM to reduce boot up time. Frequently or currentlyaccessed multimedia files may also be stored in the NVM for playback sothat the rotating media may be powered down to decrease powerconsumption. Other data to be stored in the NVM may include runtime dataand hybrid disks with shingled rotating media (or a shingled rotatingmedium) may store shingled management data in the NVM.

Shingled disks may increase the capacity by having more tracks. This maybe done by having the tracks overlapped, in a shingled form. Dependingon the size of the write head, when writing data to a track, subsequentadjacent tracks may be affected. To prevent overwriting of data, datamay be written in an appending fashion or having those data that may beaffected copied somewhere and then written back later.

Tracks on the shingled disks may be grouped into bands, with a bandcontaining multiple contiguous tracks. Between bands, there may beprovided guard areas which may not contain data. The guard areas mayallow the last track of a band to be written without affecting tracks inthe subsequent band.

To allow random writes on shingled disk, a shingled translation layermay be required. Data may be appended to the shingled disk and theshingled translation layer may map the logical location of the data to aphysical location on the disk. When the data is updated, the new datamay be appended to the disk, the old data may be invalidated, and thelocation of the data may be re-mapped to the new physical location.

Since old invalidated data may be left on the disk, the shingledtranslation layer may also provide a reclamation process to reclaim thespace occupied by the invalid data. This may involve moving only thevalid data from one location to another and updating the mapping ofthese data. According to various embodiments, a careful design of theshingled translation layer may be provided such that the mapping andcleaning of data do not impact the performance of the shingled disk toomuch.

According to various embodiments, a hybrid shingled writing disk may beprovided. A hybrid shingled drive may include some amount of fast accessnon-volatile memory (NVM; in other words: solid state drive) as well asa rotating media that contains shingled tracks. Part of the NVM may beused for storing information/meta-data related to shingled datamanagement. The disk may include a Hybrid Data Manager that may managedata between the NVM and the rotating media and a Shingled TranslationLayer (STL) that handles data access to the shingled rotating media andmaps logical address to physical location on the disk.

Tracks on shingled writing disks may be organized as multiple data bandsof several contiguous shingled tracks with a guard band in between eachdata band to prevent the data writing in one band from affecting data inanother. The shingled disk may also include one spare band with afraction of the size of a regular band, for example to temporarily storedata in case any of the data band cannot be cleaned in time to storefurther data.

Each track in the data band may be made up of multiple write unitscalled data blocks, containing multiple contiguous sectors. The mappingof logical address to physical location by the STL may be done at thedata block level. The meta-data for keeping the mapping information maybe kept in the NVM together with other metadata required by the shingledtranslation layer. According to various embodiments, a full map with anentry for every logical block may be used, wherein the blocks may besequentially arranged by LBA.

Each band may also maintain optional invalid block information thatindicates which logical data addresses are being stored in each physicalblock within each data bands. The physical blocks may be arrangedsequentially according to each data band for fast lookup. It may also bepossible to get invalid block information of a data band by looking atthe mapping table. If the shingled device have additional processingresource to generate the invalid block information when needed, invalidblock information may not need to be kept in the NVM.

Each data band may also have its own metadata which is stored in theNVM, including a Write pointer and a Wrapped-Around point (or pointer).The write pointer may point to where the next data will be appended, andthe Wrapped-Around point may indicate the point where writes can bewrapped around when the write pointer reaches the end of the band. Thedata band may also maintain a Reclaim pointer within each data band toindicate the data block where the next space reclamation routine willstart scanning from. When writes wrapped around in the data band, newwrites may be allowed as long as the distance between the data writingblock and the next block to be reclaimed (indicated by Reclaim pointer)maintains a safe “guard distance”.

A space reclamation routine may run periodically to free up spaces takenup by blocks that have been invalided. The space reclamation routine maystart reclaiming blocks from the beginning of the band and like datawriting, may be wrapped around once it reaches the end of the band. Thereclamation process may read multiple tracks, for example 10 tracks,starting from the Reclaim pointer and then may append the valid blocksat where the Write pointer is. When reclaiming the spare band, blocksmay be written back to their designated data band instead.

The reclamation routine may be interrupted by user request afterreading/writing a track to limit the effect of the reclamation on theuser response to reading or writing of one track. When the reclamationis interrupted during reading, the data read may be stored in the NVMand writing of these data may be issued as low priority requests to beprocess after the user requests.

The space reclamation routine may limit the copying of entire tracks ofvalid blocks and append them back to the band. When entire tracks ofvalid data are found at the top of the data band, those tracks may bedesignated as “inactive data” region. When new writes wrapped around,they may be appended to below the inactive region instead of startingfrom the top of the data band. This may make the cleaning routine moreefficient by not moving lots of data when no invalid blocks can befreed. The reclamation routine may always start from the beginning ofthe data band regardless of whether it contains an “inactive data”region.

The reclamation routine may begin band selection and cleaning when thedisk is I/O (input/output) idle and may only be activated when the diskis spinning. To maintain low power consumption, the reclamation routinemay not spin up the disk to reclaim invalided blocks.

According to various embodiments, devices and methods for a shingledwriting disk/shingled magnetic recording for a hybrid disk may beprovided.

According to various embodiments, architecture designs and methods tostore data in hybrid shingled writing disk may be provided.

FIG. 1A shows storage controller 100 according to various embodiments.The storage controller 100 may be configured to control storage of datain a pre-determined area of a storage medium. The storage controller 100may include a memory 102 configured to store a write pointer 104, areclaim pointer 106, and a wrapped around pointer 108. The write pointer104 may indicate a location of the storage medium to write incomingdata. The reclaim pointer 106 may indicate a location of the storagemedium to perform a space reclamation. The wrapped around pointer 108may indicate a location of the storage medium where writing is tocontinue if writing of data reaches an end of the pre-determined area.

In other words, the storage controller 100 may include pointers tolocations on the storage medium of the storage device indicating whereon the storage medium writing incoming data should be performed, where aspace reclamation (procedure or process) should be performed, and whereprocessing (writing or space reclamation) should continue of an end ofan area, in which processing is performed, is reached.

FIG. 1B shows a storage controller 110 according to various embodiments.Similar to the storage controller 100 of FIG. 1A, the storage controller110 may include a memory configured to store a write pointer 104, areclaim pointer 106, and a wrapped around pointer 108. The storagecontroller 110 may further include a space reclamation circuit 112, likewill be described in more detail below. The storage controller 110 mayfurther include an inactive data determiner 114, like will be describedin more detail below. The storage controller 110 may further include aspare location writing circuit 116, like will be described in moredetail below. The storage controller 110 may further include a sparelocation reading circuit 118, like will be described in more detailbelow. The memory 102, the space reclamation circuit 112, the inactivedata determiner 114, the spare location writing circuit 116, and thespare location reading circuit 118 may be coupled with each other, likeindicated by lines 120, for example electrically coupled, for exampleusing a line or a cable, and/or mechanically coupled.

According to various embodiments, the space reclamation circuit 112 maybe configured to read data at the location indicated by the reclaimpointer 106, may be configured to determine whether the data is outdateddata (in other words: invalid data), and to write the data to thelocation indicated by the write pointer 104 if the data is not outdateddata (in other words: if the data is valid data).

According to various embodiments, the space reclamation circuit 112 mayfurther be configured to change the reclaim pointer 106 to indicate alocation of the storage media after the location at which the data wasread.

According to various embodiments, the space reclamation circuit 112 mayfurther be configured to change the write pointer 104 to indicate alocation of the storage media after the location at which the data waswritten if the data is not outdated data.

According to various embodiments, the inactive data determiner 114 maybe configured to determine whether a region of non-outdated data ispresent at the beginning of the pre-determined area and furtherconfigured to change the wrapped around pointer 108 to a location afterthe region of non-outdated data if the region of non-outdated data ispresent at the beginning of the pre-determined area.

According to various embodiments, the spare location writing circuit 116may be configured to write data to be written in the pre-determinedregion in a spare location of the storage medium if the spacereclamation circuit 112 is not able to finish space reclamation beforethe data are to be written.

According to various embodiments, the spare location reading circuit 118may be configured to read data from the spare location of the storagemedium and write the data to the location indicated by the write pointer104 after the space reclamation circuit 112 finished space reclamation.

According to various embodiments, the space reclamation circuit 112 mayfurther be configured to continue space reclamation at the locationindicated by the wrapped around pointer 108 if space reclamation of thespace reclamation circuit 112 reaches the end of the pre-determinedarea.

According to various embodiments, the storage medium may include or maybe a shingled rotating medium.

According to various embodiments, the memory may include or may be anon-volatile memory.

FIG. 1C shows a flow diagram 122 illustrating a storage control methodof controlling storage of data in a pre-determined area of a storagemedium. In 124, a memory may be controlled to store a write pointer, areclaim pointer, and a wrapped around pointer. The write pointer mayindicate a location of the storage medium to write incoming data. Thereclaim pointer may indicate a location of the storage medium to performa space reclamation. The wrapped around pointer may indicate a locationof the storage medium where writing is to continue if writing of datareaches an end of the pre-determined area.

According to various embodiments, the storage control method may furtherinclude: reading data at the location indicated by the reclaim pointer;determining whether the data is outdated data; and writing the data tothe location indicated by the write pointer if the data is not outdateddata.

According to various embodiments, the storage control method may furtherinclude: changing the reclaim pointer to indicate a location of thestorage media after the location at which the data was read.

According to various embodiments, the storage control method may furtherinclude changing the write pointer to indicate a location of the storagemedia after the location at which the data was written if the data isnot outdated data.

According to various embodiments, the storage control method may furtherinclude: determining whether a region of non-outdated data is present atthe beginning of the pre-determined area; and changing the wrappedaround pointer to a location after the region of non-outdated data ifthe region of non-outdated data is present at the beginning of thepre-determined area.

According to various embodiments, the storage control method may furtherinclude: writing data to be written in the pre-determined region in aspare location of the storage medium if the space reclamation is notable to be finished before the data are to be written.

According to various embodiments, the storage control method may furtherinclude: reading data from the spare location of the storage medium; andwriting the data to the location indicated by the write pointer afterthe space reclamation is finished.

According to various embodiments, the storage control method may furtherinclude: continuing space reclamation at the location indicated by thewrapped around pointer if processing of the space reclamation reachesthe end of the pre-determined area.

According to various embodiments, the storage medium may include or maybe a shingled rotating medium.

According to various embodiments, the memory may include or may be anon-volatile memory.

A hybrid hard disk drive may include some relatively smaller amount offaster access non-volatile memory storage media to complement the slowerbut larger storage capacity of a rotational magnetic recording diskmedia. The fast non-volatile memory storage media may be in the form ofmemory chips embedded into the disk drive controller board.

FIG. 2 shows an overview of a hybrid hard disk drive 200 (which may alsobe referred to as hybrid drive). The hybrid hard disk drive 200 mayinclude a magnetic media 202, a spindle and R/W (read/write) electronics204, a DRAM (dynamic random access memory) 206, a hard disk controller208, and a NVM (non-volatile memory) cache 210. The to a host may beserved from NVM cache 210. The spindle and R/W electronics 204 may befurther turned off for additional power saving.

FIG. 3 shows an illustration of data types in a non-volatile memory 300according to various embodiments. In accordance with a non-volatilememory (NVM) management, a hybrid storage device may utilize the NVM fortemporary and medium term/frequently accessed data storage, whiletransferring the data to the disk storage for long term storage. Fourtypes of data may be stored in the NVM 300 to improve performance and/orreduce power consumption as shown in FIG. 3. The NVM 300 of the hybriddisk may be used to keep the following data types: boot data andfrequently accessed applications 302, application runtime data and smallread/write data 304, multimedia files 306 such as movies or songs thatare frequently or currently accessed, and data and metadata 308 relatedto shingled management. The data and metadata 308 related to shingledmanagement may include metadata 310, data 312 of less than 4 KB to bewritten, and reclamation data 314.

According to various embodiments, a hybrid shingled disk may beprovided.

FIG. 4 shows an illustration 400 of an overview of a hybrid shingleddisk according to various embodiments. A standard file system 402 may,for example using a SAS/SATA (Serial Attached SCSI (small computersystem interface)) Interface 404, access a SMR (shingled magneticrecording) disk 408, which may include a SMR management module 406. Thestandard file system 402 may use the SMR disk 408 like a regular disk inany system. The SMR disk 408 may be included in a hybrid drive which mayfor example include the SMR and a NVM (non-volatile memory; in otherwords: a solid state drive (SDD)). The SMR management module 406 mayprovide a Shingle Translation Layer (STL).

FIG. 5 shows an illustration 500 of the architecture of a hybridshingled writing disk 504 according to various embodiments. The hybridshingled writing disk 504 may include a hybrid data manager 506 whichmay manage access to an NVM 510 and to a shingled rotating media 512.The hybrid data manager 506 may decide if a read/write request is sentto the NVM 510 or the rotating media 512. The rotating/magnetic media512 may have tracks that are shingled (in other words: partiallyover-lapping). The hybrid shingled writing disk 512 may also include aShingled Manager 508 which may act as a Shingled Translation Layer (STL)to manage data on the shingled disk 512. The STL may adopt an addressre-mapping data placement scheme which may map a logical address of adata to a physical location on the disk 512. When data is written to theshingled disk 512, the data may be appended to the disk 512 and thephysical location where the data is appended may be mapped to thelogical address of the data. To read back the data, the Shingled Manager508 may look up the mapping and may issue a read for the physicallocation where the data resides. This mapping information may be storedas part of the shingled management metadata in the NVM 510 (and may forexample be referred to as C4 in FIG. 3). Small writes may also bebuffered in the NVM 510 before being flushed to the rotating media andappended to the disk 512. The Shingled Manager 508 may also include aspace reclamation (in other words: garbage collection (GC)) routine toreclaim back the space occupied by data that have been invalidated whentheir logical address have been re-mapped to another physical location.

Alternatively, the rotating media 512 may also include a small portionof tracks that are non-shingled and may be randomly accessed just likethe conventional hard disk. This may be similar to Banded drives wherethe rotating media contains both shingled and non-shingled tracks. Thenon-shingled portion may be used to store the shingled management data,metadata and buffering of small read/writes instead of using the NVM atthe cost of some performance degradation.

The Shingled Manager (STL) 508 may perform data allocation, addressmapping, invalid blocks tracking, and space reclamation.

According to the adopted hybrid disk architecture according to variousembodiments, a 1 TB disk may need about 2 GB for shingled metadata.Shingled metadata may be accessed frequently and may be critical, sothat a reliable storage with fast access may be used for shingledmetadata. Shingled metadata may impact performance if stored on nonshingled region of disk (for example, too much disk seeks may beperformed.). According to various embodiments, NVM of the hybrid diskmay be used to store metadata. The NVM may also be used for buffering ofwrite data smaller than 4 KB and/or buffering of space reclamation data.

According to various embodiments, a shingled data layout, like will bedescribed in the following, may be provided.

According to various embodiments, data may be provided in data bands,like will be described in the following.

Tracks on shingled writing disks may be organized as multiple data bandsand each band may include multiple contiguous shingled tracks. A guardband may be arranged in between each data band to prevent the datawriting to the current band from erasing data in its adjacent band.According to various embodiments, the data bands may or may have not thesame size, the same number of tracks, and capacity may or may not varyfrom band to band. The data bands may be layout such that each bandboundary is aligned to the track boundary and the bands are layout suchthat the first data band is on the outer most of the disk platter andthe last data band is in the inner most of the platter.

According to various embodiments, a data band may be handled as circularlog. According to various embodiments, with respect to data allocation,during reclamation valid data may be re-appended back to the same band,like will be described in more detail below. According to variousembodiments, it may be determined how much over-provision in each databand should be provided. Space for un-writeable region when wrappedaround may be provided. According to various embodiments, provisions maybe provided to delay run-time reclamation. Some bands may be morefrequently written/updated than others.

A small portion of the tracks in each data band may be used asover-provision which may be designed to improve the performance and notconsidered part of the capacity of the data band. A data band thereforemay include more physical blocks than the amount of addressable logicalblocks. The amount of over-provision in each band may be fixed orvariable.

According to various embodiments, over provision in data bands may beprovided. For example, 1% of the disk capacity may be provided as (over)provision for data bands, which may be distributed proportionately toall bands. Over-provision within each band may be 1% of the band size.Circular log, used for un-writable region, may be facilitated. Moreblocks update may be allowed. Runtime of reclamation may be delayed. Forexample, for a 10 GB data band, over-provision may be 100 MB (about 200tracks or 25, 600 4 KB blocks).

The shingled disk may also include another over-provision in the form ofa spare band. In some other shingled disks, there may be multiple sparebands that are left empty so that valid data from other bands can becopied over during the space reclamation process, which may be referredto as round-trip housekeeping routine. These spare bands may be similarto other bands and may have the same capacity.

According to various embodiments, the spare band may only be a fractionof the size of a regular band, and there may be only one spare bandthroughout the entire disk. The purpose of the spare band may be totemporarily store data in case any of the data band cannot be reclaimedin time to store further data. It may act as a form of insurance whenthe over-provision within the data band is unable to handle heavy writerequest for the data band.

According to various embodiments, about 1% to 1.5% of the disk capacitymay be provided as a spare band, which may act as “extra insurance”. Forexample, more active data band fills up faster (as every update may be anew append). It may be impossible to know which bands will be moreactive and allocate more provision. Therefore, a spare band may be ashared location to temporary hold data in case any data band cannot beappended in time, and may prevent runtime reclamation on very activeband.

The total over-provision may amount to about 2% to 2.5% of the entirecapacity of the rotating media, which may be less than the size of aregular data band. Part of this provision may be used to form the spareband and the others will be distributed among the data bands. Each databand may have about 1% of their tracks as over-provision, and the spareband may have a size of about 1% to 1.5% of the total capacity of theentire disk. As an example, a 1 TB rotating media can have about 20 databands, each about 50.5 GB (including provision) and a spare band that isabout 10 GB to 15 GB in size.

FIG. 6 shows an illustration 600 of a data band design and layout. Databands may be of various sizes (which for example may be space efficient)with band boundary aligned to track boundary. A first band may beprovided on outer most tracks, and a last band may be provided on innermost tracks (similar to traditional HDD). Block 602 and 604 show anexample of a number of tracks required if data band size is adopted tobe 600 MB fixed for all the zones inside a disk drive. Block 602 shows1024 tracks required for zone 0 which has 1200 sectors per tracks. Block604 shows 1228.8 tracks required for zone 10 which has 1000 sectors pertrack. The actual tracks required is 1229 and the last 0.2 track will bewasted. A case where the disk drive adopts a variable sized data banddesign is shown in block 606 and 608, meaning that for zone 0, the databand size is 600 MB while for zone 10 the data band size is 500 MB.Block 608 shows that if 500 MB is chosen as the band size, exactly 1024tracks are need for 500 MB, and no space will be wasted.

In the following, data track and data blocks according to variousembodiments will be described. Each track in the band may be made up ofmultiple write units called data blocks, and each block may include ormay consist of multiple contiguous sectors. If a track does not containexact multiple of blocks, the partial of the block on the next track isconsider to belong to the previous track (like shown in FIG. 7, whichshows an illustration 700 of blocks that form a logical track, whereintwo adjacent tracks 602 and 604 are shown, and the first partial blockof the subsequent track 604 is considered a part of the last block ofthe previous track 602). However, if the last block in the data band isnot a complete block, the partial block may be discarded as “roll-over”to the guard band area may not be allowed. Capacity wasted by thediscarded last partial blocks may be negligible when the block size issmall, since the number of bands in the disk is not large. Data tracksin a band may try to follow as closely to the physical track as possiblebut may not be restricted by the physical geometry. Tracks within a databand may not be the same number of data blocks per track due to the“roll-over” of partial data blocks.

According to various embodiments, handling of 4 KB blocks may beprovided on tracks. Management of track in a data band may always be inmultiple of 4 KB. Roll over partial blocks onto next physical track maybe provided. However, no roll over for the last partial block in theband may be provided.

The mapping of logical address to physical location by the ShingledManager may be done at the data block level; therefore, the larger theblock size, the lesser the metadata required to keep track of thelogical-to-physical mapping. However, the mapping may be at a coarsergranularity and more buffering in the NVM may be needed for small writesbefore a data block can be appended to the rotating media. An examplesize of a block may be 4 KB and 8 sectors.

In the following, data allocation according to various embodiments willbe described. According to various embodiments, data may be allocated tothe data bands sequentially, with the smallest addresses allocated tothe first data band and the largest addresses allocated to the last databand. This may provide a preservation of some form of locality andsimilarity to the way data are layout in conventional hard disks.

According to various embodiments, allocation to bands may be provided byLBA (logical block address) range (which may for example preservelocality, like HDD). The smallest LBA may be allocated in a first databand, and the largest LBA in a last data band. This may preventcontiguous LBA written in different time to be appended in differentdata band and may lead to cross data bands seeks when reading. Validdata re-appended back to the same band during space reclamation may beprovided.

According to various embodiments, metadata for shingled data managementmay be provided. Each data block may include data associated with somecontiguous sectors of logical addresses. The logical addresses of theshingled disk may be divided into blocks of similar size and each ofthese logical blocks may have a corresponding mapping to a physicalblock on the disk. The mapping information may be stored in the NVMtogether with other metadata required by the shingled translation layer.The physical mapping may be broken down in to Band ID and Block IDwithin the band. According to various embodiments, a full map with anentry for every logical block may be provided and used. To preventscanning through the mapping table when looking up the physical locationof a logical block, the mapping information may be kept at specificaddress in the NVM sorted according to the logical block address (LBA).

According to various embodiments, metadata for address re-mapping schememay be designed to use a full direct map. One entry for each addressmapped may be provided, and may be accessed directly without scanningthrough mapping table. This may allow fast access and updates. Forexample, addresses may be mapped in 4 KB blocks. A map by sector resultsin large metadata. Writes of less than 4 KB may be cached in NVM andappended later.

FIG. 8 shows an illustration 800 of a structure of logical-to-physicalmapping tables. In a first table 802, an offsets in the NVM are assignedto LBA in a sequential arrangement of LBA. The first table may beimplicitly provided by the arrangement of the data in the NVM, and maynot be actual metadata. In a second table 804, an assignment of the LBA(given for example implicitly by the offset in NVM as illustrated in thefirst table 802) to Band ID and block ID within the band. The secondtable 804 may be metadata stored in the NVM. LBA which are not writtenmay have an invalid band and block ID, for example “xx”.

FIG. 8 shows the structure of the mapping table given a 4 KB block size(8 sectors of LBA). The LBA of the logical block may be sequentiallyarranged, and therefore may not be stored as part of the metadata. Forexample if the mapping table is stored at address 00xxaa00 in the NVM,and each mapping entry requires k bytes, then the location where theband-block information are stored will be at the following address inthe NVM.

LBA 0 00xxaa00 LBA 8 00xxaa00 + k bytes offset LBA 16 00xxaa00 + 2kbytes offset

FIG. 9 shows an illustration 900 of the mapping information as shown inFIG. 8, wherein k=4.

According to various embodiments, the mapping information may besequentially arranged by every 4 KB of LBA. For example, for a 1TB diskwith 16 data bands, 1 GB of mapping data may be provided.

Write requests smaller than the block size may be buffered in the NVM(see area C4 in FIG. 3) and appended to the disk when the entire blockis in the NVM or during periodic flushing of NVM data to the media.

Each band may also maintain optional invalid block information at adesignated memory location in the NVM as described with reference toFIG. 10.

FIG. 10 shows an illustration 1000 of a layout of invalid blockinformation in NVM according to various embodiments. The invalid blockinformation may be sequentially arranged by band and block, for examplelike indicated by 1004 for blocks in a band X (for example band 0), andin 1006 for a subsequent band X+1 (for example band 1). An addressoffset in NVM may be given, like indicated by 1002. The invalid blockinformation may store LBA at specific blocks, and may be used forreclamation. For example for a 1 TB disk with 16 Data Band, 1 GB invalidblock data may be provided.

The (invalid block) information may indicate which logical dataaddresses are being stored in each physical block within each databands. The physical blocks may be arranged sequentially according toeach data band and block for fast lookup. The “xxxx” may indicate aninvalid LBA address, which may be used to denote that the data at thatparticular block has been invalidated. When data is appended as aphysical block to the disk (eg. Block 2 in Band X), the starting logicaladdress of the data that is being appended will be store in the locationthat reflects that physical block. The invalid block information is usedby the space reclamation routine to update the mapping table in FIG. 8when a particular block is being copied elsewhere.

Since data are allocated sequentially, it may also be possible to getinvalid block information of a data band by looking at the mapping table(as shown in FIG. 8). For example, if m blocks of data are allocated toband 0 and next n blocks of data are allocated to band 1, invalid blockinformation of band 1 may be generated by getting n entries startingfrom the m^(th) entry from the mapping table. The entries can then besorted by band-block ID and the original position of the entry mayindicate the LBA, while those entries without valid Band-Block ID may beconsidered invalid blocks. If the shingled device has additionalprocessing resource to generate the invalid block information as andwhen needed, then the space required in the NVM for storing shingledmanagement metadata may be reduced by not storing invalid blockinformation in the NVM.

For 4 KB write unit size, each entry may be represented by 4 Bytes (BandID uses 1 Byte, Block ID uses 3 Bytes, LBA uses 4 Bytes). To allow BlockID to be represented with 3 Bytes, each data band should not be morethan 64 GB when the block size is 4 KB. For a 1 TB disk, the capacityrequired for storing the mapping table and invalid block information maybe around 2 GB since each of the structures has 1TB/4 KB number ofentries.

In the following, management within a data band according to variousembodiments will be described.

In the following, appending data according to various embodiments willbe described.

FIG. 11 shows an illustration 1100 of appending data according tovarious embodiments. For example, processing for one data band is shownin FIG. 11. Each data band may have its own metadata which may be storedin the NVM, including a Write pointer 1108 and a Wrapped-Around point1106. Data appended to the data band may be written to where the writepointer 1108 points to. The position of the write pointer 1108 may bemoved whenever data blocks are appended to the data band and may alwaysindicate the block where the next data will be appended. TheWrapped-Around point 1106 may indicate the point where writes may bewrapped around when the write pointer 1108 reaches the end of the bandand is set initially as the beginning of the data band. Written blocks1102 are shown as blocks filled with doth. Unwritten (or cleaned) blocks1104 are shown as empty blocks.

In the following, wrapped around writes according to various embodimentswill be described. In a conventional data band management, when the databand is fully written, no data will be allowed to be written to the banduntil the whole data band is completely cleaned by the space reclamationroutine. According to various embodiments, the data bands may be cleanedin portions and new data may be written to partially cleaned data bands.This may be done by maintaining a Reclaim pointer within each data bandto indicate the data block where the next reclamation routine will startscanning from. As shown FIG. 11 above, after writing the last block ofthe data band, the write pointer 1108 may wrap around and repositions tothe Wrapped-Around point 1106 to continue with the data writing. Writesmay be allowed as long as the distance between the data writing blockand the next block to be reclaimed (indicated by a reclaim pointer aswill be described in more detail below) maintains a safe “guarddistance” such that the data write will not erase previously writtenregion that have not been reclaimed by the reclamation routine. The“guard distance” may be similar to the area formed by the fixed guardband between two data bands. Storage space utilization efficiency may beincreased since the “un-writable” region is the “guard distance” insteadof an entire data band.

FIG. 12 shows an illustration 1200 of a data band, illustrating wrappedaround write to a reclaimed area of the data band. FIG. 12 shows a databand that is partially reclaimed and data writes that have wrappedaround. A reclaim pointer 1212 may indicate where the previousreclamation routine ended. Should the reclamation be unable to reclaimand free up blocks in time to allow new writes into the data band, datamay be temporary written to the spare band and copied back to thedesignated data band later. Similar to FIG. 11, a wrapped around point1208, and a write point 1210 are shown. Written blocks 1202 and 1206 areshown as blocks filled with dots. Unwritten (or cleaned) blocks 1204 areshown as empty blocks.

In the following, space reclamation within a data band according tovarious embodiments will be described. Data may be written to the databand in an appending fashion and the old blocks (in other words: blocks,in which data that is deleted or re-written was stored) may beinvalided. This may result in many invalid blocks within the data band.These invalid blocks may never be accessed but take up space. Therefore,there may be a need to periodically free up areas occupy by theseinvalid blocks. Written blocks in the data band may be read and thevalid blocks may be appended as new writes back to the data band, andthe area previously occupied by those blocks may be freed up and beavailable for use. The Reclaim pointer in the data band may keep trackof where the next reclaim will begin and also may mark where theprevious reclaim ends at.

The space reclamation routine may start reclaiming from the beginning ofthe band and like data writing, may wrap around once it reaches the endof the band. The reclamation routine may read multiple tracks, forexample 10 tracks, starting from the reclaim pointer and then may appendthe valid blocks at where the write pointer is. If the data band beingreclaimed is the spare band, then the valid blocks are appended back totheir designated band instead. Should there be an incoming user requestduring the reclamation process; the reclamation routine may interruptthe reading/appending process after completing reading/writing thecurrent track to allow the user request to proceed. The effect of thereclamation on the user response may thus be limited to the reading orwriting of one track. When the reclamation routine is interrupted duringreading, the data blocks read may be stored in the NVM and writing ofthese blocks may be issued as low priority requests to be process afterthe user requests. When the reclamation routine is interrupted during aread (e.g. after reading 4 tracks), it may not continue with reading ofmore tracks once the process resumes, instead, the reclamation routinemay ensure those data blocks that have been read and stored in the NVMare written to the disk before beginning another round of read andappend.

Since data allocation may be by logical addresses, it may be possiblethat a data band contains both active and inactive data. Inactive dataare those that are not updated and therefore blocks associated with themremains valid once written. According to various embodiments, the spacereclamation routine may be efficient by limiting the copying of entiretracks of valid data blocks and appending them back to the band. Thismay be done by setting the top part of a band as “inactive data” regionand moving the Wrapped-Around point to lower part of the band just belowthe “inactive data” region. Whenever the reclamation routine begins fromthe beginning of the band, there may be a chance that the “inactivedata” region can be determined and the Wrapped-Around point set. If thereclamation routine discovered that the top few tracks contain onlyvalid data blocks, then those tracks are left intact (see for exampleFIG. 13A, like will be described below). The first track from thebeginning of a band that contains invalid blocks may be the track thatthe reclamation routine will start reclaiming and where theWrapped-Around point will be set subsequently. When the Write pointerwrapped around, it may begin at the position indicated by theWrapped-Around point instead of the beginning of the data band as shownin FIG. 13B below.

Once the Reclaim pointer reaches the end of the data band, it may startscanning from the beginning of the data band and re-determine if theWrapped-Around point needs to be reset. If the previous “inactive data”have invalid blocks, then the reclamation may start from the first trackthat contains invalid blocks and the Wrapped-Around point adjustedaccordingly. “Inactive data” that have been slowly gathered at the topof the band may ensure that the space reclamation routine works moreefficiently by skipping tracks of valid data when reclaiming invaliddata blocks from the data bands.

FIG. 13A shows an illustration 1300 of inactive data 1302 (illustratedby hatched blocks) skipped by the reclamation routine. Reclamation ofthe inactive data 1302 may be skipped, and reclamation may start afterthe inactive data, like indicated by 1310. Similar to FIGS. 11 and 12,the reclaim pointer 1312, and the write pointer 1314 are shown. Writtenblocks 1306 are shown as blocks filled with dots. Unwritten (or cleaned)blocks 1304 and 1308 are shown as empty blocks. Blocks with inactivedata 1302 (in other words: inactive written blocks) are shown as blocksfilled with dashes (in other words: filled with horizontal lines).

FIG. 13B shows an illustration 1316 of write wrapped around at thewrapped-around point. Like in FIG. 13A, inactive data 1302 (indicated byblocks with horizontal lines), the write point 1314, and the reclaimpointer 1312 are shown. The wrapped-around point 1310 may be (directly)after the inactive data 1302. Written blocks 1318 and 1322 are indicatedby blocks filled with dots, and unwritten (or cleaned) blocks 1320 areillustrated by empty blocks.

The track based space reclamation routine according to variousembodiments may be used from 1 to n (with an integer number n) number oftracks (for example 10 tracks). It may stop after finish reading/writingcurrent track when user requests arrive to make the best use of eachrotation. It may limit impact on user request to at most 1 trackread/write. Valid data blocks read may be temporarily stored in NVM andmay be appended back to data band immediately if I/O idle, otherwiseprocess after user requests.

According to various embodiments, an “Inactive data” region within adata band may be provided. It may be created during reclaim process.Data may be set as “inactive” data if all blocks on the correspondingtrack are valid and skipped when reclaiming the track. Thewrapped-around point may be set below (or after) “inactive” area sowrites may skip the “inactive” area. “Inactive data” may be Re-checkevery time the space reclamation process wraps around. No requesthistory may be required to determine “inactive” data. The “inactivedata” region may only be at beginning of a data band.

The inactive data region may reduce moving of large chunks of data whilereclaiming only little or no invalid blocks (in other words: may reduceinefficiency), and may reduce reclamation time especially when disk/bandis near full.

Example savings from “Inactive data” region may be as follows. A 0.5 GBmovie file may be stored across about 1000 tracks. It may be a read-onlyfile, therefore no invalid blocks; each reclaim cycle may be 10 tracks.The movie file may require 100 reclaim cycles to move/re-write it. Each10 track reclaim cycle may include 10 tracks read and 10 tracks write,18 single track switch, and 1 half data band seek. A total of 2.5 secmay be used per cycle. So for 100 reclaim cycles, about 4 min may beused.

According to various embodiments, a data band for reclaiming invaliddata blocks may be selected. The shingled disk may include multiple databands and the space reclamation routine may select a data band toreclaim. The reclamation routine begins band selection and reclaimingwhen the disk is I/O idle. To maintain low power consumption, thereclamation routine may be active only when the disk is spinning. If thedisk has gone into power down mode, the reclamation routine may not spinup the disk to do reclamation. The reclamation routine may selects adata band for reclaiming (in other words: for performing reclamation)based on the following order:

1) Least % of writable blocks;

2) Most % of invalid+% of blocks in spare band;

3) Band closest to current read/write head.

Writable blocks may refer to blocks that can be written safely. When thewrite pointer has wrapped around, writable blocks may take into accountthe blocks making up the “guard distance” between the write pointer andthe reclaim pointer.

According to various embodiments, a “guard distance” may be providedwhich has similar use as the “floating band” mention above. “guarddistance” is a distance which could be in terms of number sectors/trackswithin a data band to prevent data over-writing. To determine whetherthe data can be appended to the write pointer, it may be desired tocheck that the distance between the current write block and the appendpointer (in other words: reclaim pointer) where there are kept validdata is bigger than the “guard distance”. If not (in other words: if thedistance is not provided), it is not allowed to write as this may erasevalid data on the disk. Or else (if the distance is provided), it isallowed to write. The distance between the current write location to theappend pointer keeps on changing as the reclamation process can claimmore space, in addition, data can be kept on appending to the writepointer. Both of them can cause the “guard distance” or “guard band” tokeep on moving within the data band, therefore it is like a “floatingband”. However, the “guard distance” may not be a full data band, butrather a few tracks within a data band to prevent over-writing of datawithin the data band. This may save space by disallowing writes only toarea that may be over-written due to the size of the write head, ratherthan wasting entire band as “guard”.

The spare band according to various embodiments may be configured totemporary hold data when the data band cannot be written safely. Thismay happen when there are too many updates in the same data band suchthat the over-provision is used up and the reclamation routine cannotreclaim invalid data blocks in the band in time. Data written to thespare band may be moved back to their respective data band only duringthe reclamation of the spare band. A disk may have only one spare bandor a plurality of spare bands.

According to various embodiments, devices and methods may be providedfor determining how the fixed range of addresses can be divided into themultiple section, for example, by dividing disk addresses into bandssequentially. The data bands may be layout on the disk from outer toinner diameter, such that smaller addresses may be in bands near theouter diameter and larger addresses may be in bands near the innerdiameter. This may be to follow as closely as possible to the wayconvention disk arrange physical block address (PBA).

According to various embodiments, if the writes are big enough, they maybe appended sequentially to the band in data block units. This mayimprove efficiency by writing data once and allows sequential writes forlarge requests.

According to various embodiments, track based space reclamation may beprovided. There may be a maximum number of tracks to clean during eachreclamation, but this number may be lesser if there are incoming userrequests. This may ensure that user response is not impacted too greatlyduring space reclamation, and that the reclamation routine may be moreefficient by allowing large sequential read and write during when diskis I/O idle.

According to various embodiments, mixed hot and cold (active andinactive) data in the same data band may be provided, and the bands maybe of varying sizes.

According to various embodiments, there may be no need to keep track ofpast write request to identify hot data. A regular space reclamationroutine and time to “filter” the inactive data to the top of the bandand “freezing” the portion may be provided to reduce a need to reclaiminactive data blocks.

The identification of hot and cold data according to various embodimentsmay be to have different garbage collection/space reclamation methodsfor data bands containing different types of data. A space reclamationmethod may be provided, in which the creation of inactive data regionmay be to reduce inefficient reclamation effort in moving large chunksof inactive data when such effort does not reclaim and free up muchinvalid blocks.

According to various embodiments, a shingled magnetic recording mediummay be provided which may be used like traditional HDD (hard diskdrive). It may have a comparable performance and minimum cost. A datamanagement scheme may be provided. Writing and updating (RMW or Addressre-mapping) may be provided. The impact of reclamation (for example whendisk is near full) may be reduced. A metadata design may be provided forfast access (for example for searching and/or updating) at low size (forexample to be kept in NVM).

A track based data band design may be provided. A metadata design may beprovided for log based, address re-mapping data placement. Provision andspare bands may be provided. Managing data band as circular log may befacilitated. Run-time reclamation on very active data bands may bereduced. A space reclamation method may be provided. The impact to userrequests during reclamation may be limited. Reclamation time may bereduced when disk/band is near full.

According to various embodiments, a log based, address remapping dataplacement may be provided. It may not cause large write amplificationlike read-modify-write scheme. Blocks with data updated may beinvalidated and may be reclaimed periodically. Data bands may be managedas circular log. They may be partially cleaned while still in use. Notnecessarily extra data bands may be needed for garbage collection/spacereclamation (i.e. there is no need to move valid blocks to another bandto free up a band).

According to various embodiments, an address re-mapping scheme may beprovided. Metadata for address mapping and invalid block information forspace reclamation may be provided. Efficient space reclamation methodsmay be provided.

According to various embodiments, provision may be provided. Accordingto various embodiments, capacity wastage by provision may be reduced.Capacity wastage according to various embodiments compared to methodusing extra bands will be described in the following, e.g. for a 1 TBdisk with 20 data bands with each about 50 GB. A method requiring extrabands for space reclamation may using 2 Extra Bands (i.e. 100 GB), whichmay be 10% of 1 TB According to various embodiments, band provision andspare band may make up only about 2.5% of 1 TB.

According to various embodiments, variable data band sizes may allowmaximum tracks and blocks to be used. Metadata may be kept as fulldirect map in NVM. Fast and direct access with scanning of mapping tablemay be provided. A hybrid structure with NVM for buffering small writesand reclamation data may be provided. Two layers of over provision (withless than about 2.5% of the disk capacity) may be provided. Every bandmay have some provision. A shared band as extra insurance may be used byany band. According to various embodiments, there may be no need for anextra band for reclamation.

According to various embodiments, a track based reclamation method maybe provided. “Inactive data” regions to improve space reclamationefficiency may be determined. No analysis of historic requests may beneeded to identify inactive regions.

In the following, computations and calculations with respect to variousembodiments will be described.

NVM storage required for Mapping Table (4 KB write unit size) may be asfollows:

-   -   Band ID: 1 Byte (2⁸, 0˜255);    -   Block ID: 3 Bytes (2²⁴, 0˜16,777,215).

The maximum number of representable entries in a data band may be16,777,216 entries. When each entry (block) represents 4 KB, a maximumsize in a data band may be 16,777,216*4 KB=64 GB.

Storage required for storing mapping of one data band may be16,777,216*4 Byte=64 MB. 1TB capacity may require 16 data bands, and thetotal storage for mapping may be 16*64 MB=1 GB.

NVM storage required for Invalid Block Information (for LBA by 4 KB) maybe as follows:

-   -   LBA: 4 Byte (2³², 0˜4,294,967,295 sectors).

1 sector may include 512 Byte.

The maximum number of sectors for 1TB capacity may be 1TB/512Byte=2,147,483,648 sectors.

Block size may be 4 KB, therefore LBA may be stored for every 8 sectors.1 TB may be broken down into 268,435,456 of 8 sectors/4 KB.

Storage required for storing invalid block information may be268,435,456*4 Byte=1 GB.

Computations for over-provision will be described in the following.

A total of about 2 to 2.5% of capacity may be used for over-provision.For 1TB capacity, about 20 to 25 GB may be used for over-provision.

1% of the capacity may be allotted to data bands for over-provision. For64 GB data band, additional provision may be about 640 MB, equivalent toabout 163,840 4 KB data blocks.

About 1 to 1.5% of the capacity may be allotted to a spare band. Thespare band may have a capacity of about 10 to 15 GB, which may be about16% to 24% of the size of a data band.

In the following, computations with respect to a creation (ordefinition) of “inactive data” regions according to various embodimentswill be described. For example, a video file with about 0.5 GB in size,and each track having about 0.5 MB capacity may be considered.

The video may be stored across about 1000 tracks. If each reclaim cycleis 10 tracks, 100 reclaim cycles may be required to scan through theregion occupied by the video file.

If the video file is a read only movie file, no blocks may beinvalidated (as there may be no updates), and each reclaim cycle mayread 10 tracks and append the 10 tracks. This may translate to:

a) 10 tracks read+10 tracks write;

b) 18 single track seek (9 for reading, 9 for writing); and

c) 1½ data band seek (assuming that the write pointer is ½ data bandaway from reclaim pointer).

If the tracks occupied by the video file are considered the “inactivedata” region, the total savings may be 100 reclaim cycles.

In the following, a Comparison of search complexity for entries storedin different structures will be described. n may denote the number ofentries in table. O(x) may denote the big O notation (which may also bereferred to as Landau notation), and may mean that the order ofmagnitude O(x) is not much bigger than x.

For a hash table, there may be a best case of O(1), and a worst case ofO(n).

Only mapping of LBA that is already on disk may be kept, and the numberof entry may depend on how much data may be written to the disk.

For a direct map, the complexity may be of O(log n). Only mapping of LBAthat is already on disk may be kept, and the number of entries maydepend on how much data is written to disk. Assuming entries are alreadysorted, it only may be scanned for an entry. When all entries exist onthe map (which may mean that the map becomes a full direct map), searchmay become O(1). If the entries are not sorted, finding an entry mayrequire linear search, which may be O(n).

For a full direct map, complexity may be O(1). An entry of the mappingfor all possible LBA may be kept on disk, regardless if that data hasbeen written to disk. According to various embodiments, wastage may bemaximum 7 sectors (3.5 KB) per data Band, which may add up to less than70 KB if the disk has 20 Bands. This may be in addition to the 2.5%over-provision.

A multilevel map may provide a complexity in the best case of O(k),where k may be the number of levels. Only mapping of LBA that is alreadyon disk may be kept, and the number of levels may be fixed regardless ofthe number of data written to disk. (for example may be 1^(st) levellook for the Band Id, 2^(nd) level look for the Block Id. According tovarious embodiments, the metadata design may be a full direct map. Themultilevel map may be an alternative according to various embodiments.For metadata designed to keep the information of bandID and blockID, atwo level map and searching may be provided. When searching forparticular block/LBA, it may be desired to look for bandID first, whichmay be called the 1^(st) level search. Once the bandID has allocated,blockID has to be found out from the particular band. Here, this may bereferred to as the 2^(nd) level search. Time complexity may depend onwhat type of map is implemented at each level, and the best case may bewhen every level is O(1).

FIG. 14 shows an illustration 1400 of a multilevel map. A map 1402 for afirst level is shown, and maps 1404 and 1406 for a second level areshown.

Other structures (except full direct map) may include a savings ofstorage space used. The size occupied may depend on number of entries inthe Map/Table. A full direct map may already have space reserved for allentries; therefore the size may be fixed.

In the following, a capacity wastage of fixed size data band accordingto various embodiments will be described. A difference in the sectorsper track between the 1^(st) and last zone of a disk may be 40%. Forsimplicity, a constant difference of 30 sectors per track (spt) betweeneach zone may be assumed. For example, a disk may include 20 Zones. Thenumber of sectors per track may be as follows:

-   -   Zone 0=2000 spt;    -   Zone 1=1970 spt;    -   Zone 2=1940 spt; . . . and

Zone 19=1430 spt.

A data band size of 50 GB may be assumed. Furthermore assuming that theentire band fits into a zone, space wasted for each band in that zonemay be like stated in Table 1.

TABLE 1 Zone Band KB/Track Number of tracks KB on last track of Band isin in Zone used for Band Used Wasted 0 1000 52429 800 200 1 985 53228205 780 2 970 54051 300 670 3 955 54900 255 700 4 940 55776 300 640 5925 56680 725 200 6 910 57615 60 850 7 895 58580 595 300 8 880 59579 160720 9 865 60612 285 580 10 850 61681 800 50 11 835 62789 820 15 12 82063938 460 360 13 805 65129 760 45 14 790 66366 450 340 15 775 67651 50725 16 760 68986 200 560 17 745 70375 170 575 18 730 71821 200 530 19715 73327 710 5

In addition to the above, any remaining tracks that cannot form up aband may be wasted. A maximum wastage may be the remaining 73326 tracksin last zone, which may be wastage of 49.999 GB (5%). If the size of thedata band is 100 GB, the possible max wastage may increase to 99.999 GB(10%). Different geometry and band sizing may give different wastage.Most of the wastage may come from tracks that are unable to form up acomplete data band.

More wastage may be present if data bands cannot cross zone. Forexample, using the table above, if Zone 0 has 60000 tracks, theremaining 7571 tracks (7.2 GB) may be wasted since they cannot form up a50 GB data band.

While the invention has been particularly shown and described withreference to specific embodiments, it should be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims. The scope of the invention is thusindicated by the appended claims and all changes which come within themeaning and range of equivalency of the claims are therefore intended tobe embraced.

What is claimed is:
 1. A storage controller configured to controlstorage of data in a predetermined area of a storage medium, the storagecontroller comprising: a memory storing a write pointer that indicates alocation of the storage medium to write incoming data, storing a reclaimpointer that indicates a location of the storage medium to perform aspace reclamation, and storing, before writing of data reaches an end ofthe predetermined area, a wrapped around pointer that indicates alocation of the storage medium where writing is to continue if writingof data reaches the end of the predetermined area.
 2. The storagecontroller of claim 1, further comprising: a space reclamation circuitconfigured to read data at the location indicated by the reclaimpointer, configured to determine whether the data is outdated data, andto write the data to the location indicated by the write pointer if thedata is not outdated data.
 3. The storage controller of claim 2, whereinthe space reclamation circuit is further configured to change thereclaim pointer to indicate a location of the storage media after thelocation at which the data was read.
 4. The storage controller of claim2, wherein the space reclamation circuit is further configured to changethe write pointer to indicate a location of the storage media after thelocation at which the data was written if the data is not outdated data.5. The storage controller of claim 1, further comprising: an inactivedata determiner configured to determine whether a region of nonoutdateddata is present at the beginning of the predetermined area and furtherconfigured to change the wrapped around pointer to a location after theregion of nonoutdated data if the region of nonoutdated data is presentat the beginning of the predetermined area.
 6. The storage controller ofclaim 2, further comprising: a spare location writing circuit configuredto write data to be written in the predetermined region in a sparelocation of the storage medium if the space reclamation circuit is notable to finish space reclamation before the data are to be written. 7.The storage controller of claim 6, further comprising: a spare locationreading circuit configured to read data from the spare location of thestorage medium and write the data to the location indicated by the writepointer after the space reclamation circuit finished space reclamation.8. The storage controller of claim 2, wherein the space reclamationcircuit is further configured to continue space reclamation at thelocation indicated by the wrapped around pointer if space reclamation ofthe space reclamation circuit reaches the end of the predetermined area.9. The storage controller of claim 1, wherein the storage mediumcomprises a shingled rotating medium.
 10. The storage controller ofclaim 1, wherein the memory comprises a non-volatile memory.
 11. Astorage control method of controlling storage of data in a predeterminedarea of a storage medium, the storage control method comprising:storing, in a memory, a write pointer that indicates a location of thestorage medium to write incoming data; storing, in the memory, a reclaimpointer that indicates a location of the storage medium to perform aspace reclamation; and storing, in the memory and before writing of datareaches an end of the predetermined area, a wrapped around pointer thatindicates a location of the storage medium where writing is to continueif writing of data reaches the end of the predetermined area.
 12. Thestorage control method of claim 11, further comprising: reading data atthe location indicated by the reclaim pointer; determining whether thedata is outdated data; and writing the data to the location indicated bythe write pointer if the data is not outdated data.
 13. The storagecontrol method of claim 12, further comprising: changing the reclaimpointer to indicate a location of the storage media after the locationat which the data was read.
 14. The storage control method of claim 12,further comprising: changing the write pointer to indicate a location ofthe storage media after the location at which the data was written ifthe data is not outdated data.
 15. The storage control method of claim11, further comprising: determining whether a region of nonoutdated datais present at the beginning of the predetermined area; and changing thewrapped around pointer to a location after the region of nonoutdateddata if the region of nonoutdated data is present at the beginning ofthe predetermined area.
 16. The storage control method of claim 11,further comprising: writing data to be written in the predeterminedregion in a spare location of the storage medium if the spacereclamation is not able to be finished before the data are to bewritten.
 17. The storage control method of claim 16, further comprising:reading data from the spare location of the storage medium; and writingthe data to the location indicated by the write pointer after the spacereclamation is finished.
 18. The storage control method of claim 12,further comprising: continuing space reclamation at the locationindicated by the wrapped around pointer if processing of the spacereclamation reaches the end of the predetermined area.
 19. The storagecontrol method of claim 11, wherein the storage medium comprises ashingled rotating medium.
 20. The storage control method of claim 11,wherein the memory comprises a non-volatile memory.
 21. A tangible,non-transitory computer readable medium comprising: a predetermined areafor storage of data; a write pointer that indicates a location of thepredetermined area to write incoming data; a reclaim pointer thatindicates a location of the predetermined area to perform a spacereclamation; and a wrapped around pointer that is stored before writingof data reaches an end of the predetermined area and that indicates alocation of the predetermined area where writing is to continue ifwriting of data reaches the end of the predetermined area.